This invention relates to a switch having a seesaw type movable contact blade.
FIGS. 1A and 1B show an example of the prior art switch having a movable contact blade configured to be moved through a seesaw motion in a vertical cross-sectional view taken parallel to the major side of the switch and in a vertical cross-sectional view taken parallel to the minor side, respectively. A metallic support plate 60 is passed vertically through and secured to the bottom panel 12 of the box-like case 10 made of electrically insulating plastic material generally in the center thereof. The support plate 60 has upstanding guide projections 611 and 612 extending from the top end edge thereof at the opposite sides between which a movable contact blade 50 is swingably mounted on the top end edge. The top end edge of the support plate 60 serves as a fulcrum for the swinging movement of the movable contact blade 50 while the lower end portion of the support plate 60 extending outside of the bottom panel 12 defines a movable contact blade terminal 6T which is electrically connected by contact with the movable contact blade 50.
Attached to the undersurface of the movable contact blade 50 adjacent one end thereof is a movable contact 50C. An inverted L-shaped fixed contact blade 70 is disposed on the bottom panel 12 of the case such that the upper horizontal leg 72 of the fixed contact blade 70 is in opposition to the undersurface of the movable contact blade 50 while the vertical leg of the blade extends as a fixed contact blade terminal 7T downwardly out through the bottom panel 12. The upper horizontal leg 72 of the fixed contact blade 70 has a fixed contact 70C attached thereto in opposition to the movable contact 50C.
A tumbler type actuator 40 is disposed over the movable contact blade 50 so as to close the top opening 10A of the case 10. The actuator 40 has pivot studs 47 extending from the opposite side walls thereof which are received in bearing holes 16 formed in the opposite side walls 11 of the case 10. The actuator 40 further has an integral columnar portion 42 extending downwardly from the undersurface of the tumbler body in the center thereof The columnar portion 42 has a spring housing bore 42A formed therein in which a coil spring 45 is accommodated. A plunger 43 has its upper end portion inserted in the housing bore 42A and engaged by the coil spring 45 to be downwardly biased so that the lower end of the plunger 43 is always urged to be in sliding engagement with the upper surface of the movable contact blade 50 by the biasing force of the coil spring 45.
In FIG. 1A, the tumbler type actuator 40 is illustrated as being depressed in its switch-off position in which the lower end of the plunger 43 presses down on the upper surface of the movable contact blade 50 on the side of the support plate 60 opposite from the movable contact 50C to stably hold the movable contact 50C opened from the fixed contact 70C so that there is no electrical continuity between the terminals 6T and 7T. When the actuator 40 is pressed toward its switch-on position, it is turned clockwise as viewed in the drawing about the studs 47 so that the lower end of the plunger 43 is slidingly moved up the upper surface of the movable contact blade 50 toward and beyond the upper end of the support plate 60 against the spring force of the coil spring 45 to go over to the portion of the upper surface of the blade on the side of the movable contact 50C whereupon the movable contact blade 50 is swung to bring the movable contact 50C into abutment with the fixed contact 70C to thereby stably hold the switch in the on-position. As a result, the terminals 6T and 7T are kept in electrical continuity.
While in this prior art switch the contact is established between the undersurface of the movable contact blade 50 and the straight top end edge of the support plate 60, a complete line contact is not realized but there are actually a plurality of point contacts. Further, the positions of the contact points will change with the swinging movement of the movable contact blade 50 and may also move due to a mechanical shock or vibration, so that the electrical stability of the switch has not been satisfactory. In addition, since substantially all of the voltage across the terminals 6T and 7T is applied between the contacts 50C and 70C, the switch had the disadvantage that it was attended with an expedited wearing out of the contacts 50C and 70C due to discharge sparks during the making and breaking of the contacts.
It is an object of this invention is to provide a switch with a seesaw type movable contact blade which has a high withstandingness to voltage and which ensures a reduced wearing out of the contacts due to sparks occurring during the switching of the switch and is electrically stable.
The switch according to this invention comprises:
a box-like case having a bottom panel of an insulator and an opening in the top thereof;
a support plate secured to and extending vertically upwardly from the bottom panel and terminating in a top end edge defining a central convex portion which is the highest in the center thereof;
a movable contact blade formed of a generally quadrilateral metallic plate supported on the top end edge of the support plate for rotating movement about the top end edge defining a pivot axis and having attached thereon two movable contacts spaced apart in the direction of the pivot axis adjacent one end of the blade;
two fixed contact blades affixed at one end to the bottom panel and each having a fixed contact attached thereto adjacent the one end in opposition to a corresponding one of the movable contacts with the other end portion of each fixed contact blade extending out through the bottom panel to define a terminal;
a driving means having two sliding protrusions pressing on the upper surface of the movable contact blade and slidable in a direction perpendicular to the direction of the pivot axis;
coil spring means having a biasing force to urge the driving means toward the movable contact blade;
a rotatable actuator having a spring housing bore formed in the lower end portion in which the coil spring means is accommodated and including a columnar portion adapted to hold the driving means retractably in abutment with the movable contact blade as the driving means is slidingly moved on the movable contact blade; and
a cover means mounted so as to close the top opening of the case and having an aperture formed therethrough in the center thereof for rotatably holding the actuator which is inserted through the aperture;
whereby rotation of the actuator selectively establishes and break electrical continuity between the terminals between the two fixed contacts.